JavaScript 2D array grouping: is there a more elegant/optimized way?

Question

I have the following code which works just fine. I'm just wondering if there's a more elegant/optimized way of doing so.

Long "code" short, given the data:

var myArray = [
  ['X', 'A', 0, 1, 'Y', 3],
  ['X', 'A', 4, 5, 'Y', 6],
  ['X', 'B', 6, 5, 'Y', 4],
  ['X', 'B', 3, 2, 'Y', 1],
  ['X', 'C', 7, 8, 'Y', 9],
];

Say I want to group by column index 1 and only sum column indexes 2, 3, 5.

Expected result is:

[
  ["A", 4, 6, 9],
  ["B", 9, 7, 5],
  ["C", 7, 8, 9]
]

// data
var myArray = [
  ['X', 'A', 0, 1, 'Y', 3],
  ['X', 'A', 4, 5, 'Y', 6],
  ['X', 'B', 6, 5, 'Y', 4],
  ['X', 'B', 3, 2, 'Y', 1],
  ['X', 'C', 7, 8, 'Y', 9],
];

// col that I want to group by
var colIndex = 1;

// cols I want to sum
var colsToSum = [2, 3, 5];

var arrayGroupBy = function(myArray, colIndex, colsToSum) {

  // get unique column values
  var uniqueValues = [];
  myArray.forEach(function(row) {
    if (uniqueValues.indexOf(row[colIndex]) === -1) {
      uniqueValues.push(row[colIndex]);
    }
  });

  var newData = [];
  uniqueValues.forEach(function(value) {

    // get filtered rows
    var filteredRows = myArray.filter(function(row) {
      return row[colIndex] === value;
    });

    var row = [value];

    // columns to sum
    colsToSum.forEach(function(num) {
      if (filteredRows.length === 1) {

        // push single row
        row.push(filteredRows[0][num]);

      } else {

        // sum row cols
        var total = filteredRows.reduce(function(sum, current) {
          return sum + current[num];
        }, 0);

        row.push(total);
      }

    });

    newData.push(row);
  });

  return newData;
};

console.log(arrayGroupBy(myArray, colIndex, colsToSum));

Unfortunately I can't use ES6 on this one...

Thanks!

name not found · Accepted Answer · 2017-02-15 01:52:46Z

I tried to find a solution for your question. There would be many good ES6 features which would make the solution a bit more readable/cleaner. But here is a solution without any ES6 features:

var groupBy = function(myArray, colIndex, colsToSum) {
  var obj = {};
  myArray.forEach(function(e) {
    if(!obj.hasOwnProperty(e)) {
      obj[e[colIndex]] = new Array(colsToSum.length + 1)
        .join('0').split('').map(parseFloat);
      }
  });

  myArray.forEach(function(row) {
    for (var i = 0; i < colsToSum.length; i++) {
      obj[row[colIndex]][i] += row[colsToSum[i]];
    }
  });

  return Object.keys(obj).map(function(key) {
    return [key].concat(obj[key]);
  });
}

Explanation:

An object with the properties 'A', 'B' and 'C' will be created.
An array [0, 0, 0] will be assigned to each property.
Loop myArray and colsToSum and add the values to the right object property
Convert the object to an array and return it

Maybe there are better solutions :)

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